The influence of climate regime shift on ENSO

Observations indicated that for the El Niño/Southern Oscillation (ENSO) there have been eastward displacements of the zonal wind stress (WS) anomalies and surface heat flux (short wave heat flux and latent heat flux) anomalies during El Niño episodes in the 1981–1995 regime relative to the earlier regime of 1961–1975 (without corresponding displacements during La Niña episodes). Our numerical experiments with the Zebiak–Cane coupled model generally reproduced such displacements when the model climatological fields were replaced by the observed climatologies [of sea surface temperature (SST), surface WS and surface wind atmospheric divergence] and simulated climatologies (of oceanic surface layer currents and associated upwelling) for the 1981–1995 regime. Sensitivity tests indicated that the background atmospheric state played a much more important role than the background ocean state in producing the displacements, which enhanced the asymmetry between El Niño and La Niña in the later regime. The later regime climatology state resulted in the eastward shifts in the ENSO system (WS and SST) only during El Niño, through the eastward shift of the atmosphere convergence heating rate in the coupled model. The ENSO period and ENSO predictability were also enhanced in the coupled model under the later regime climatology. That the change in the mean state of the tropical Pacific atmosphere and ocean after the mid 1970s could have produced the observed changes in ENSO properties is consistent with our findings.     

海温气候平均场的改变及其对ENSO事件划分的影响

比较了将于2003年1月投入我国海温监测业务使用的Reynolds海温1971－2000年气候平均场和原有系统中海温气候平均场的差别，并分析了7个关键区海温指数的变化，最后，以NINO3区海温指数为例，分析了对历史上厄尔尼诺和拉尼娜事件划分的差别。     

与夏季北太平洋副热带中尺度海洋涡旋相联系的海气关系

采用高分辨率卫星和再分析资料,利用涡旋探测技术、滤波和合成分析等方法,对夏季北太平洋副热带地区中尺度海洋涡旋与大气的耦合关系进行了分析。结果表明:在日时间尺度上,海洋涡旋的海表温度（Sea SurfaceTemperature,简称SST）与海表风速之间不仅存在同位相的正相关关系,还存在反位相的负相关关系,即在涡旋这种中尺度上既存在海洋对大气的强迫,也存在大气对海洋的强迫。海表风速与SST同位相时,对暖（冷）涡来说,向上（下）的净热通量增强,云和降水增多（减少）;其海水温度异常和海流旋度较强,暖（冷）涡较为深厚,一定程度上表明了海洋对大气的强迫。海表风速与SST反位相时,对暖（冷）涡而言,当其处在正（负）位势高度异常、中低层相对湿度较小（大）、气温较高（低）的大气配置下,海表风速较小（大）;同时向下（上）净热通量增强,云和降水减少（增多）;涡旋海水温度异常和海流旋度较弱,这种暖（冷）涡较为浅薄;表明晴空（阴雨）条件下有利于暖（冷）涡的维持,一定程度上反映了大气对海洋的强迫作用。     

A study on air–sea interaction on the simulated seasonal climate in an ocean–atmosphere coupled model

This study investigates the effects of air–sea interaction upon simulated tropical climatology, focusing on the boreal summer mean precipitation and the embedded intra-seasonal oscillation (ISO) signal. Both the daily coupling of ocean–atmosphere and the diurnal variation of sea surface temperature (SST) at every time step by accounting for the ocean mixed layer and surface-energy budget at the ocean surface are considered. The ocean–atmosphere coupled model component of the global/regional integrated model system has been utilized. Results from the coupled model show better precipitation climatology than those from the atmosphere-only model, through the inclusion of SST–cloudiness–precipitation feedback in the coupled system. Cooling the ocean surface in the coupled model is mainly responsible for the improved precipitation climatology, whereas neither the coupling itself nor the diurnal variation in the SST influences the simulated climatology. However, the inclusion of the diurnal cycle in the SST shows a distinct improvement of the simulated ISO signal, by either decreasing or increasing the magnitude of spectral powers, as compared to the simulation results that exclude the diurnal variation of the SST in coupled models.     

Precipitation over eastern South America and the South Atlantic Sea surface temperature during neutral ENSO periods

The dominant mode of coupled variability over the South Atlantic Ocean is known as “South Atlantic Dipole” (SAD) and is characterized by a dipole in sea surface temperature (SST) anomalies with centers over the tropical and the extratropical South Atlantic. Previous studies have shown that variations in SST related to SAD modulate large-scale patterns of precipitation over the Atlantic Ocean. Here we show that variations in the South Atlantic SST are associated with changes in daily precipitation over eastern South America. Rain gauge precipitation, satellite derived sea surface temperature and reanalysis data are used to investigate the variability of the subtropical and tropical South Atlantic and impacts on precipitation. SAD phases are assessed by performing Singular value decomposition analysis of sea level pressure and SST anomalies. We show that during neutral El Niño Southern Oscillation events, SAD plays an important role in modulating cyclogenesis and the characteristics of the South Atlantic Convergence Zone. Positive SST anomalies over the extratropical South Atlantic (SAD negative phase) are related to increased cyclogenesis near southeast Brazil as well as the migration of extratropical cyclones further north. As a consequence, these systems organize convection and increase precipitation over eastern South America.     

On the interannual variability of surface salinity in the Atlantic

The mechanisms controlling the interannual variability of sea surface salinity (SSS) in the Atlantic are investigated using a simulation with the ECHAM4/OPA8 coupled model and, for comparison, the NCEP reanalysis and an observed SSS climatology. Anomalous Ekman advection is found to be as important as the freshwater flux in generating SSS anomalies, in contrast to sea surface temperature (SST) anomalies which are primarily caused by surface heat flux fluctuations. Since the surface heat flux feedback does not damp the SSS anomalies but generally damps existing SST anomalies, SSS anomalies have a larger characteristic time scale. As a result, they are more influenced by the mean currents and the geostrophic variability, which dominate the SSS changes at low frequency over much of the basin. The link between SSS anomalies and the dominant patterns of atmospheric variability in the North Atlantic sector is also discussed. It is shown that the North Atlantic Oscillation generates SSS anomalies much more by Ekman advection than by freshwater exchanges. At least in the coupled model, there is little one-to-one correspondence between the main atmospheric and SSS anomaly patterns, unlike what is found for SST anomalies.     

赤道东太平洋地区海温的随机模拟

本文对描述海气相互作用的随机模型作进一步的解释,考虑周期性外力对海气系统的影响,并用这一改进随机进随机动力模型对赤道东太平洋地区的海温作随机模拟,模拟序列的解释方差达到70%。试验表明,考虑周期性外力对海气系统的作用是明显的,它能进一步提高模拟效果,使随机模型更接近实际。      

Assessment of the Capability of ENSEMBLES Hindcasts in Predicting Spring Climate in China

Using the hindcasts provided by the Ensemble-Based Predictions of Climate Changes and Their Impacts(ENSEMBLES) project for the period of 1980–2005, the forecast capability of spring climate in China is assessed mainly from the aspects of precipitation, 2-m air temperature, and atmospheric circulations. The ENSEMBELS can reproduce the climatology and dominant empirical orthogonal function(EOF) modes of precipitation and 2-m air temperature, with some differences arising from different initialization months. The multi-model ensemble(MME) forecast of interannual variability is of good performance in some regions such as eastern China with February initialization.The spatial patterns of the MME interannual and inter-member spreads for precipitation and 2-m air temperature are consistent with those of the observed interannual spread, indicating that internal dynamic processes have major impacts on the interannual anomaly of spring climate in China. We have identified two coupled modes between intermember anomalies of the 850-hPa vorticity in spring and sea surface temperature(SST) both in spring and at a lead of 2 months, of which the first mode shows a significant impact on the spring climate in China, with an anomalous anticyclone located over Northwest Pacific and positive precipitation and southwesterly anomalies in eastern China.Our results also suggest that the SST at a lead of two months may be a predictor for the spring climate in eastern China. A better representation of the ocean–atmosphere interaction over the tropical Pacific, Northwest Pacific, and Indian Ocean can improve the forecast skill of the spring climate in eastern China.     

Influence of sea surface temperature on the intraseasonal variability of the South China Sea summer monsoon

The objective of this study is to examine, based on recently available high resolution satellite and observational data, the evolution and role of sea surface temperature (SST) in influencing the intraseasonal variability of the South China Sea (SCS) summer monsoon (SM). The study focuses on the 30–60?day timescale when the northward propagating anomalies are dominant over the SCS. Composite analysis of the SST maximum events during SCS SM shows that increased SST anomalies over the SCS are significantly influenced by the downward shortwave radiation flux anomalies, with the suppressed surface latent heat flux anomalies supplementing to it. A thermal damping of the positive SST anomalies induces positive upward heat fluxes, which then destabilize the lower atmosphere between 1,000 and 700?hPa. The positive SST anomalies lead the positive precipitation anomalies over the SCS by 10?days, with a significant correlation (r?=?0.44) between the SST-precipitation anomalies. The new findings here indicate an ocean-to-atmosphere effect over the SCS, where underlying SST anomalies tend to form a favorable condition for convective activity and sustain enhanced precipitation during the SCS SM. It is also argued, based on our observations, that the negative sea level pressure anomalies induced by the positive SST anomalies play a role in enhancing the northward propagation of the intraseasonal anomalies over the SCS.     

Delayed Atmospheric Temperature Response to ENSO SST： Role of High SST and the Western Pacific

Tropical zonally symmetric atmospheric warming occurs during ENSO’s warm phase, and lags the equa- torial east Pacific sea surface temperatures (SSTs) by 3–4 months. The role of the Indian and Atlantic oceans on the atmospheric delayed response has been pointed out by earlier studies. For 1951–2004, a regression analysis based on the observed SST data shows the western Pacific has a similarly important role as the Indian and Atlantic. Nevertheless, there is time mismatch of around 1–2 months between the zon...     

印度洋对ENSO事件的响应:观测与模拟

观测事实显示,在El Ni(n～)o期间,伴随着赤道中东太平洋表层海温(SST)的升高,热带印度洋SST出现正距平.作者利用海气耦合模式模拟了印度洋对ENSO事件的上述响应,并进而讨论了其物理机制.所用模式为法国国家科研中心Pierre-Simon-Laplace 全球环境科学联合实验室(IPSL)发展的全球海气耦合模式.该模式成功地控制了气候漂移,能够合理再现印度洋的基本气候态.观测中与ENSO相关的热带印度洋SST变化,表现为全海盆一致的正距平,并且这种变化要滞后赤道中东太平洋SST变化大约一个季度,意味着它主要是对东太平洋SST强迫的一种遥响应,模式结果也支持这一机制,尽管模式中的南方涛动现象被夸大了,使得模拟的与ENSO相关联的SST正距平的位置南移,阿拉伯海和孟加拉湾被负距平(而不是正距平)所控制.研究表明,东太平洋主要通过大气桥影响潜热释放来影响印度洋SST变化.赤道东太平洋El Ni(n～)o事件的发展,导致印度洋上空风场异常自东而西传播;伴随着风场的变化,潜热发生相应变化,并最终导致SST异常的发生.非洲东海岸受索马里急流控制的海域,其SST的变化不能简单地利用热通量的变化来解释.证据显示,印度洋的增暖是ENSO事件发生的结果而不是其前期信号.     

华南冬季准静止锋年际变异特征及其对东亚气候的影响

基于JRA55再分析资料、观测的降水量和海表温度等数据,利用统计诊断方法分析了华南冬季气候准静止锋的主要变异特征,并探讨了其与环流、海温及东亚气候的联系。华南冬季气候准静止锋的主要变异模态表现为强度变异模态和经向位置变异模态,它们以年际变化为主。类东部型ENSO海温异常及热带中西印度洋海温异常对华南准静止锋强度的年际变异有显著影响;而类中部型ENSO海温异常型显著影响着华南气候准静止锋的南北位置。华南冬季准静止锋的强度变异对东亚副热带地区的降水、以及我国东部内陆地区的近地面气温有显著影响;华南冬季准静止锋南北位置变异则显著影响我国江淮流域降水、以及我国华南至东南沿海一带的近地面气温。华南冬季准静止锋的强度变异模态对东亚的降水和近地面气温的影响范围较位置变异模态都要大。     

黄渤海一次持续性大雾过程特征和成因分析

利用日本MTSAT1R卫星数据、常规地面和高空观测数据、NCEP FNL客观再分析资料和NEARGOOS（NorthEast Asian Regional Global Ocean Observing System）的海表温度（SST）数据,分析了2010年5月31日至6月5日发生在黄渤海及周边地区的一次持续性海雾天气的形成、维持、消散特征及其物理机制。结果表明：大雾形成前低层水汽非常充沛,入海变性冷高压的稳定维持为这次持续性海雾过程提供了有利的背景条件,海雾在夜间辐射冷却作用下形成;大雾期间黄渤海     

中国东部冬季温度异常偶极型模态的一个前兆信号

利用中国160站逐月温度、NCEP再分析、NOAA-CIRES 20世纪再分析以及NOAA海表温度等资料,分析了中国东部（100°E以东地区）冬季温度年际变化的主要模态,并重点研究了其中第2模态（即偶极型模态）的成因机理和前期信号。同时,也以2012～2013年冬季为例,探讨了这一温度异常模态的预测方法。研究主要发现:除中国东部大范围一致偏冷或偏暖模态以外,110°E以东的北方地区偏冷（暖）还经常对应着华南和110°E以西地区的偏暖（冷）,构成温度异常反向变化的偶极型模态。这种偶极型模态也是冬季气候变化的一个主要模态,2012～2013年冬季温度异常即属于这一模态。中国东部冬季温度一致型模态主要与前期秋季中东太平洋海温异常、亚洲大陆北部积雪,及其邻近的北冰洋地区海冰密集度异常联系紧密。而对于偶极型模态,海温的影响并不明显,前期秋季的东亚中纬度地区积雪、北冰洋斯瓦尔巴群岛、法兰士约瑟夫地群岛附近海域的海冰密集度异常,以及它们引起的表面温度异常分布可能具有重要贡献,其中北冰洋海冰密集度异常导致的该地区表面温度异常的影响可能更为重要。综合了海冰和积雪信号的前期秋季北冰洋—东亚温度差异（Arctic Ocean-East Asian temperature contrast,简称AE）指数与中国东部冬季温度异常偶极型模态具有显著联系,可以作为一个重要的预测因子。2012年秋季赤道中东太平洋海温的正常状态以及北冰洋暖异常和东亚中纬度地区冷异常的表面温度分布特征,都不利于中国东部冬季温度南北一致型异常的发生,而是有利于偶极型异常分布。利用AE指数可以有效地预测2012～2013年中国东部冬季温度异常特征。     

海表面盛行风背景下大气对黑潮海洋锋的响应特征

采用一系列高分辨率的卫星资料,应用高通滤波等方法,研究了春季不同海表面盛行风背景下,东海黑潮海洋锋区附近的海气关系。观测分析表明:在东海,春季3种不同海表面盛行风条件下海表面温度与海表面风速之间都存在明显的正相关关系,表现为海洋对大气的强迫作用。大气对海洋锋的响应在3种不同盛行风条件下也存在明显的差异。在西北盛行风和东南盛行风背景下,即当风向垂直于海洋锋由冷侧(暖侧)吹向暖侧(冷侧)时,海表面风的辐散(辐合)出现在海洋锋上空。同时,海洋锋对海平面气压(SLP)、降水和对流活动的影响较弱,表明大气对海洋锋的响应主要局限在大气边界层内。在东北盛行风背景下,即当风平行于海洋锋时,在海洋锋的暖(冷)水侧上空为海表面风的辐合(辐散),并与SLP的异常低(高)值相对应,主要雨带出现在黑潮暖舌上空。无论从总降水还是层云、对流降水频次的空间分布来看,盛行东北风时,海表面温度对其上雨带的影响最为明显。分析结果还表明,在不同盛行风背景下,海洋锋附近的海气关系由不同的物理机制在起主导作用。当盛行平行于海洋锋的东北风时,主要由SLP调整机制起作用;而盛行垂直于海洋锋的西北风时则主要由垂直混合机制起作用。     

Contrasting Impacts of South and North Tropical Indian Ocean Sea Surface Temperature Anomalies on East Asian Summer Climate

Using observational data and model simulations,the author find that the North Indian Ocean(NIO)sea surface temperature(SST)anomalies can trigger an eastward atmospheric Kelvin wave propagating into the equatorial western Pacific,inducing an anomalous anticyclone over the subtropical Northwest Pacific(NWP)and resulting in prominent summer climate anomalies in the East Asia-Northwest Pacific(EANWP)region.However,the response of tropospheric temperatures and atmospheric Kelvin waves to the South Indian Ocean(SIO)SST anomalies is weak;as a result,the impact of the SIO SST anomalies on the EANWP summer climate is weak.The contrasting impacts of NIO and SIO SST anomalies on the EANWP summer climate is possibly due to the different mean state of SSTs in the two regions.In summer,the climatological SSTs in the NIO are higher than in the SIO,leading to a stronger response of atmospheric convection to the NIO SST anomalies than to the SIO SST anomalies.Thus,compared with the SIO SST anomalies,the NIO SST anomalies can lead to stronger tropospheric air temperature anomalies and atmospheric Kelvin waves to affect the EANWP summer climate.     

Characteristics and vertical structure of oceanic mesoscale eddies in the Bay of Bengal

The signatures of mesoscale eddies induced surface and subsurface changes have not been comprehensively quantified for the Bay of Bengal (BoB) region. This study quantifies the statistical properties and three-dimensional (3D) eddy structures in the BoB. To accomplish this, the satellite altimetry data combined with automated eddy detection and tracking algorithm is used. Horizontal distribution of surface characteristics of eddies is analyzed by using 24 years (1993–2016) of AVHRR infrared satellite sea surface temperature (SST) and 7 years (2010–2016) of sea surface salinity (SSS) of SMOS satellite data. Surface eddy centric composite analysis reveals the existence of warm (cold) and diverse SSS anomalies for anticyclonic (cyclonic) eddies. During winter, it is important to note that the eddy induced SST and SSS anomalies show the dipole patterns show opposite phases for the cyclonic and anticyclonic eddies. Observed diploe structures are consistent with the eddy rotation and background large-scale meridional gradient of temperature and salinity fields. The 3D structure of eddies is investigated by using the ARMOR3D and Argo float profiles. The horizontal distribution of temperature and salinity anomalies from ARMOR3D signify the monopole structure of eddies in the subsurface layers. Further, the analysis of composite averages of 241 (200) Argo temperature profiles indicates the core of anticyclonic (cyclonic) eddies centered at about ∼140 m (∼100 m). However, salinity profiles depict the existence of core at ∼65 m (∼50 m). This study have practical relevance to a variety of stakeholders and finds profound importance in the validation of eddy-resolving ocean models for the BoB region.     

冬季东太平洋峡谷风的季节内变化及相联系的海气特征

基于高分辨的卫星资料和再分析资料,本文采用合成分析、相关分析和带通滤波等方法研究了季节内时间尺度上东太平洋峡谷风的变化,并首先发现冬季东太平洋峡谷风存在4~16 d的季节内变化周期。进一步分析表明在该时间尺度上峡谷风异常与局地海温异常之间的关系存在由负相关到正相关的明显转变,在峡谷风强度达到最大之前及最大时,峡谷风异常与局地海温异常之间的关系主要表现为大气对海洋的强迫作用,北风分量的加强使中高纬度干冷空气进入峡谷风地区,海表面的净热通量损失使得海温降低。在峡谷风强度达到最大之后其与局地海温异常的关系则转变为海洋对大气的强迫作用,冷海温异常可一直持续到峡谷风强度达到最大后的第六天。冷海温异常的维持使得湍流混合受到抑制,导致其上的海表面风速减小。此外,峡谷风的季节内变化可能与东太平洋至北美上空的大气环流异常及其演变有关。在湾区峡谷风达到最大之前,北太平洋海平面气压正异常逐渐东移南下并在其最大时到达墨西哥湾上空,使得北美高压增强,湾区两侧气压差增大,对应湾区峡谷风达到最大。     

Roles of Indian and Pacific Ocean air–sea coupling in tropical atmospheric variability

Sea surface temperature (SST) variations include negative feedbacks from the atmosphere, whereas SST anomalies are specified in stand-alone atmospheric general circulation simulations. Is the SST forced response the same as the coupled response? In this study, the importance of air–sea coupling in the Indian and Pacific Oceans for tropical atmospheric variability is investigated through numerical experiments with a coupled atmosphere-ocean general circulation model. The local and remote impacts of the Indian and Pacific Ocean coupling are obtained by comparing a coupled simulation with an experiment in which the SST forcing from the coupled simulation is specified in either the Indian or the Pacific Ocean. It is found that the Indian Ocean coupling is critical for atmospheric variability over the Pacific Ocean. Without the Indian Ocean coupling, the rainfall and SST variations are completely different throughout most of the Pacific Ocean basin. Without the Pacific Ocean coupling, part of the rainfall and SST variations in the Indian Ocean are reproduced in the forced run. In regions of large mean rainfall where the atmospheric negative feedback is strong, such as the North Indian Ocean and the western North Pacific in boreal summer, the atmospheric variability is significantly enhanced when air–sea coupling is replaced by specified SST forcing. This enhancement is due to the lack of the negative feedback in the forced SST simulation. In these regions, erroneous atmospheric anomalies could be induced by specified SST anomalies derived from the coupled model. The ENSO variability is reduced by about 20% when the Indian Ocean air–sea coupling is replaced by specified SST forcing. This change is attributed to the interfering roles of the Indian Ocean SST and Indian monsoon in western and central equatorial Pacific surface wind variations.     

Mechanism on how the spring Arctic sea ice impacts the East Asian summer monsoon

Observational analysis and purposely designed coupled atmosphere–ocean (AOGCM) and atmosphere-only (AGCM) model simulations are used together to investigate a new mechanism describing how spring Arctic sea ice impacts the East Asian summer monsoon (EASM). Consistent with previous studies, analysis of observational data from 1979 to 2009 show that spring Arctic sea ice is significantly linked to the EASM on inter-annual timescales. Results of a multivariate Empirical Orthogonal Function analysis reveal that sea surface temperature (SST) changes in the North Pacific play a mediating role for the inter-seasonal connection between spring Arctic sea ice and the EASM. Large-scale atmospheric circulation and precipitation changes are consistent with the SST changes. The mechanism found in the observational data is confirmed by the numerical experiments and can be described as follows: spring Arctic sea ice anomalies cause atmospheric circulation anomalies, which, in turn, cause SST anomalies in the North Pacific. The SST anomalies can persist into summer and then impact the summer monsoon circulation and precipitation over East Asia. The mediating role of SST changes is highlighted by the result that only the AOGCM, but not the AGCM, reproduces the observed sea ice-EASM linkage.